Minimally-invasive intra-cardiac ablation is the treatment of choice for various types of arrhythmias. To perform such treatment, the physician typically inserts a catheter through the vascular system into the heart, brings the distal end of the catheter into contact with myocardial tissue in areas of abnormal electrical activity, and then energizes one or more electrodes at or near the distal end in order to create tissue necrosis.
A number of systems for intra-cardiac ablation therapy are commercially available, such as the CARTO™ system offered by Biosense Webster Inc. (Diamond Bar, Calif.). CARTO tracks the position and operating parameters of the distal end of the catheter and displays this information electronically on a three-dimensional (3D) anatomical map of the heart.
U.S. Pat. No. 8,206,380, whose disclosure is incorporated herein by reference, describes a method for measuring the contact force exerted on tissue by a probe for heating the tissue and containing an antenna which is connected to a radiometer whose output reading indicates the temperature at depth of the tissue contacted by the probe. The method comprises displaying the output reading of the radiometer, applying sufficient power to the probe to heat the tissue to a selected first temperature that is not lethal to the tissue, moving the probe into contact with the tissue, observing the increase in the displayed temperature reading that occurs when the probe contacts the tissue, and advancing the probe toward the tissue until the displayed temperature reading reaches a value corresponding to a selected tissue contact force. After the probe position in the tissue has stabilized, the applied power to the probe may be increased to heat the tissue to a selected second temperature that is lethal to tissue for a sufficient time to ablate the tissue followed by lowering the tissue heating to a sub-lethal temperature.
U.S. Patent Application Publication 2012/0136348, whose disclosure is incorporated herein by reference, describes a medical method, device, and system, including advancing an ablation element of a medical device into contact with tissue to be treated, selecting a power level of energy to ablate the tissue, delivering energy at the selected power level to the ablation element, determining whether the ablation element is in continuous contact with the tissue, and reducing the selected power level when the ablation element ceases to be in continuous contact with the tissue.
PCT International Publication WO/9840023, whose disclosure is incorporated herein by reference, describes a system for ablating tissue within a body, the system having: an energy source providing a level of energy which is not damaging to the cellular structures of the body tissue, a catheter coupled to the energy source, the catheter having an electrode; and means for sensing the temperature of the electrode while also sensing the amount of energy which is not damaging to the cellular structures of the body tissue is delivered to the electrode, the sensing means coupled to the catheter and coupled to the energy source wherein the degree to which the electrode contacts the heart tissue (e.g. no contact, moderate contact, good contact or excellent contact) may be determined.